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<h1><a href="https://archiveofourown.org/works/26092486">What Lurks Beneath</a> by <a class='authorlink' href='https://archiveofourown.org/users/fifty_fifty/pseuds/fifty_fifty'>fifty_fifty</a></h1>

<table class="full">

<tr><td><b>Category:</b></td><td>Merlin (TV)</td></tr>

<tr><td><b>Genre:</b></td><td>Alternate Universe - Canon, Anal Sex, Canon Era, First Time, Fuck Or Die, M/M, Porn with Feelings, Swimming Boys, Tentacle Monsters, Tentacle Sex, Tentacle Tuesday, Tentacles, Transformation, Water</td></tr>

<tr><td><b>Language:</b></td><td>English</td></tr>

<tr><td><b>Status:</b></td><td>Completed</td></tr>

<tr><td><b>Published:</b></td><td>2020-08-25</td></tr>

<tr><td><b>Updated:</b></td><td>2020-08-25</td></tr>

<tr><td><b>Packaged:</b></td><td>2021-05-06 04:28:10</td></tr>

<tr><td><b>Rating:</b></td><td>Explicit</td></tr>

<tr><td><b>Warnings:</b></td><td>Creator Chose Not To Use Archive Warnings</td></tr>

<tr><td><b>Chapters:</b></td><td>1</td></tr>

<tr><td><b>Words:</b></td><td>1,498</td></tr>

<tr><td><b>Publisher:</b></td><td>archiveofourown.org</td></tr>

<tr><td><b>Story URL:</b></td><td>https://archiveofourown.org/works/26092486</td></tr>

<tr><td><b>Author URL:</b></td><td>https://archiveofourown.org/users/fifty_fifty/pseuds/fifty_fifty</td></tr>

<tr><td><b>Summary:</b></td><td><div class="userstuff">
              <p>He opened his eyes, searching frantically for signs of Arthur. Finally he caught sight of him, struggling below. Merlin flipped himself over, pushing down against the water, his lungs burning as he reached out to grasp Arthur’s hand.</p>
            </div></td></tr>

<tr><td><b>Relationships:</b></td><td>Merlin/Arthur Pendragon (Merlin)</td></tr>

<tr><td><b>Comments:</b></td><td>26</td></tr>

<tr><td><b>Kudos:</b></td><td>137</td></tr>

<tr><td><b>Collections:</b></td><td>Kinkalot 2020</td></tr>

</table>

<a name="section0001"><h2>What Lurks Beneath</h2></a>
<div class="story"><div class="fff_chapter_notes fff_head_notes"><b>Author's Note:</b><blockquote class="userstuff">
      <p>Written for the Kinkalot Bingo 2020 prompt Tentacles and the Team Sorcerers Tentacles Tuesday!</p>
    </blockquote></div><div class="userstuff module">
    
    <p>The journey had been miserable and perilous, but finally, they were almost there. According to Gaius and the maps, the location of the rift was somewhere within the forest that lay below. Merlin could feel the way it reached out to him; old, dark magic, tendrils curling around his heart. He shivered though it wasn’t quite nightfall yet, not looking forward to what lay ahead.</p>
<p>Morning dawned bright and early, the remains of their fire still smoldering in the center of camp. Arthur stomped it out, looking around with a frown.</p>
<p>“It’s this way,” said Merlin, pointing east. </p>
<p>“How do you know?” </p>
<p>“I just have a… feeling,” Merlin finished lamely. </p>
<p>Arthur rolled his eyes.</p>
<p>“I suppose the mighty Arthur Pendragon knows better?”</p>
<p>“Well, <i>obviously</i> we need to continue heading south, <i>Mer</i>lin. The land slopes down in that location.”</p>
<p>“What does that have to do with anything!” Merlin said, following Arthur’s lead, swinging up into Aster’s saddle.</p>
<p>“I wouldn’t expect you to understand, Merlin. You’re not a hunter. You don’t have that <i>instinct</i>. Come on. This way.”</p>
<p>After several hours heading in the downwards direction his pratness had chosen, they reached a lake. Merlin sighed in relief, surely they’d have a break here. They could let the horses drink their fill and wash away the grime and sweat of several days of traveling.</p>
<p>He slid down off his horse before Arthur could say otherwise, taking Hengroen’s reins from him, leading the horses to the water’s edge.</p>
<p>“What do you think? Do we have time for a bathe?” he asked, already toeing off his boots and socks.</p>
<p>Arthur groaned, rolling his shoulders. “Fine, I guess it won’t do any harm to be clean before riding to our deaths. Help me off with this.”</p>
<p>Merlin hurried over, nimble fingers making quick work of the various buckles and ties of Arthur’s armour and helping to ease his hauberk over his head. He left Arthur to take care of the rest, slipping off his own jacket and shirt, then with a deep breath dropping his breeches. He always felt a surge of nervous excitement being naked in front of Arthur. He knew he wasn’t too bad to look at. His body was thin, compared to the knights, but he was still strong and wiry from hours of physical labour. Not that Arthur ever would ever think about men like that, of course. Not like Merlin did. Yet another secret he kept locked up deep in his chest, only letting it have voice in the cover of night.</p>
<p>He started to stride towards the water. </p>
<p>“Race you!” called Arthur. His naked form suddenly streaking past.</p>
<p>Merlin laughed giving chase. Honestly, Arthur was such a competitive arse.</p>
<p>Soon they were both splashing and chasing each other around the lake. </p>
<p>Arthur dipped under the water mid-stroke with a yell and Merlin chuckled as he trod water.</p>
<p>“You must think I’m daft if you think I’m falling for that!” Merlin called. </p>
<p>He waited for Arthur to surface, knowing that he wouldn’t be able to hold his breath for long. The seconds passed. Still no Arthur. Merlin bit his lip. No, this was all part of Arthur’s plan. If he went to check, he’d grab him and pull him under too.</p>
<p>Okay. That was enough. Merlin started to think Arthur might actually be in trouble. He struck out and swam across the lake, taking a deep breath before diving under.</p>
<p>He opened his eyes, searching frantically for signs of Arthur. Finally he caught sight of him, struggling below. Merlin flipped himself over, pushing down against the water, his lungs burning as he reached out to grasp Arthur’s hand. Arthur gripped his fingers tightly and with several hard kicks, he suddenly came free. They broke to the surface, gasping for air.</p>
<p>“Arthur,” Merlin panted. “Are you okay?”</p>
<p>Arthur coughed vigorously, struggling.</p>
<p>“Let’s get to the shore.”</p>
<p>Merlin helped Arthur out. His eyes scanning Arthur’s face anxiously, his lips a vibrant blue.</p>
<p>“What happened?” he asked, starting to examine Arthur as Gaius had taught him. Arthur’s airway and pulse, then moving on to his head to check for a wound.</p>
<p>Arthur shivered, his body jerking on the sandy shore.</p>
<p>“Arthur?” </p>
<p>“Hurts,” groaned Arthur.</p>
<p>Merlin glanced down and blooming across Arthur’s leg and along his torso was a rapidly-spreading slimy green skin. Sorcery. It had to be.</p>
<p>“Arthur?” He cradled Arthur’s face to look at him. “Tell me what happened.”</p>
<p>“Something— Something in— in the lake,” Arthur gasped, his body arching again. Skin transforming.</p>
<p>Merlin thoughts raced, trying to recall if he’d ever read anything about magical creatures that lurked in lakes in Gaius’ bestiary.</p>
<p>The only thing he could recall was the hydros? Or the kraken? The bite of a hydros was said to make a man swell. And kraken were vast creatures, said to be as large as an island, sinking ships. Surely neither one would be lurking in a lake in Camelot.</p>
<p>Arthur cried out and Merlin glanced down as something wet and warm slid up his leg. Gone were Arthur’s legs. Replaced instead with a series of tentacles below his waist.</p>
<p>Merlin placed his hands on Arthur’s chest, ready to push his magic deep inside urging it to heal, when the tentacles ripped him off and Arthur was splayed on top of him, his tentacles roaming Merlin’s hips. Merlin shuddered, surprised to find the sensation wasn’t entirely unpleasant.</p>
<p>“Merlin,” said Arthur, his voice raw. “Merlin, I need— It hurts, I—” </p>
<p>A tentacle wrapped around Merlin’s cock and suddenly Merlin knew what the beast that had taken hold of Arthur wanted. It wanted Merlin, it wanted magic. Fertility rituals were often performed by the Priestesses of the Old Religion. Merlin had read about them in a book Gaius had tucked away on his highest bookshelf. Such rituals were performed to appease the magic of the world, by a priestess aiding in the spilling of a warlock’s seed. And apparently this beast was hungry for a sacrifice. </p>
<p>A tentacle glided down his inner thigh and between his legs, sticky and wet. It started to poke and prod at his entrance.</p>
<p>“Merlin,” Arthur choked, the slippery skin now halfway up Arthur’s chest. “I think I— If I don’t— I think I might—”</p>
<p>“Shh, shh!” said Merlin, threading his hand through Arthur’s hair, gentling him as he pulled him down for a kiss. “Do it.”</p>
<p>Merlin cried out as the limb slowly pushed its way in, stretching him wide and filling in so deep he could barely breathe. Other tendrils started to swarm his body, caressing his skin, sliding around, lifting him as the first one throbbing and swelling, started to thrust in and out of his hole. The one entwined around his cock, started to pump him in unison. </p>
<p>“Ah, Gods!” Merlin keened, his back a perfect arc as the tentacle brushed against a spot inside him. The tentacle did it again and Merlin let out a sob.</p>
<p>More of them—Merlin lost count—started to slither across his chest, pulling and sucking at his nipples, one gliding ever closer to his neck. Arthur batted it away, tilting Merlin’s face towards his. </p>
<p>As a feeler gently caressed his face, Merlin realised it was Arthur controlling the limbs, not the beast and he panted, rocking his body into Merlin’s, rolling their hips together. He brought Merlin’s face to his and pressed a kiss to his lips, as Merlin wrapped his legs around Arthur, and it deepened into something sweet and tender.</p>
<p>The tentacle—Arthur—started to lunge, pushing into him hard and fast, and Merlin’s magic, an ever present hum, started to spark and churn as heat bloomed in his gut. His legs quivered, the pressure building until he was sure he was going to explode.</p>
<p>“Merlin,” Arthur murmured, pressing his face against Merlin’s neck. </p>
<p>He felt Arthur throb deep inside him, hot and wet, flooding his insides with a choked off moan. Then he trembled as his orgasm and magic flooded through him. His cock pulsing with Arthur’s name on his lips.</p>
<p>The next thing Merlin could remember was waking to the weight of Arthur’s body on his. He ran his fingers over Arthur’s back and sides, eternally grateful as his hands reached Arthur’s arse. The beast, or curse perhaps, was gone. And a rather wonderful, warm and pert arse remained. He hurried to make a hasty retreat knowing that their act had been under duress. Arthur wouldn’t want this. And Merlin didn’t want it either if it wasn’t permitted.</p>
<p>Arthur grabbed his hand and placed it back with a hum. </p>
<p>“You okay?” he asked.</p>
<p>“Yes. I’m fine, Arthur. I’m fine.”</p>
<p>“Sorry about—”</p>
<p>“It’s okay,” said Merlin, his face heating as he felt the slickness still between his legs. </p>
<p>“But you didn’t—”</p>
<p>“I didn’t do anything I didn’t want to, Arthur.”</p>
<p>“But—” Arthur yawned, his eyes starting to droop.</p>
<p>Merlin pressed a kiss to his head. “I’d do anything for you, Arthur. Just sleep, sire. Everything else can wait.”</p>
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